1. Field of the Invention
The present invention relates to a portable radio apparatus such as a portable telephone and a portable computer, and particularly relates to battery power saving technique in a portable radio apparatus which has a battery and a backlighting type liquid crystal display unit.
2. Description of the Related Art
A portable radio apparatus such as a portable telephone and a portable computer generally includes an image display section on which transmitted or received information is displayed. Such an image display section is often made of a liquid crystal display section, which is lighted up by a lighting source such as a backlighting source to make it easy to confirm the information. When a user regards the lighting as unnecessary in the daytime, the user freely operates a button to turn off the backlighting source so that the battery power can be saved.
Another information such as use state information, for example, the reception electric field strength, the remaining battery power and so on, is also displayed in addition to the transmitted or received information. Such a use state information is effective if the user regards the information as the warning. Therefore, the lighting is wasteful when the portable radio apparatus is kept without being used, when it is ready for receiving or transmitting a radio signal, and when the user does not look at the image display section. Thus, it is desirable that a backlight is turned off by means of turning-off means in the above cases so as to save the power of the battery. It is more desirable that the use state information is not displayed to save the battery power while the information is unnecessary.
Such a desirable portable radio apparatus is described in Japanese Laid Open Patent Disclosure (JP-A-Heisei 5-327587), in which the portable radio apparatus includes an power supply control circuit provided between a liquid crystal display circuit (LCD) and a power supply circuit. A CPU controls the power supply control circuit to turn on or off the liquid crystal display circuit. According to such a known means, the battery power supply is controlled in the use state to restrain the supply of power to the LCD displaying circuit while the portable radio apparatus is kept without being used, while it is waiting to receive, and while communication is performed.
By the way, the above reference has no significant ideas as to how the CPU determines whether the portable radio apparatus is kept without being used, it is ready to receive transmission data, or it is communicating. Another problem to be solved remains in which since the power supply control circuit is added, the number of parts increases so that the portable radio apparatus becomes complicated, resulting in high manufacture cost.
In addition to the above reference, a technique for battery saving is disclosed in Japanese Laid Open Patent Disclosure (JP-A-Heisei 4-263305), in which no supply of display data to a LCD display section is detected such that the supply of battery power to the LCD display section is stopped, and the battery power supply is restarted by contact detecting means.
In Japanese Laid Open Utility Model (JU-A-Showa 61-66897), a backlight is turned on for a predetermined time period after a key is operated.
In Japanese Laid Open Patent Disclosure (JP-A-Heisei 6-140979), the technique is described in which a photo-sensor is provided and the message display is turned off in a dark place.